1. Field of the Invention
The invention relates generally to the field of downhole pipe cutting tools. More specifically the invention relates to methods and devices for cutting piping downhole using an abrasive water jet.
2. Background Art
Tubular members, for instance, coiled tubing, production tubing, drill pipe, and other items with a hollow space typically may be cut from the inside by inserting a cutting device into the interior hollow space. Hydrocarbon producing wellbores are often lined with tubular members, such as casing, that may be cemented into place within the wellbore. Wellbores may often include additional equipment such as packers and other well completion devices that are secured within a wellbore. Either by design, through wear-and-tear, or by acute damage, these tubular members and other equipment may become unusable and require replacement. Often, a tubular member is secured to the wellbore, and the tubular member must be radially severed at some point along its length in order to remove it from the wellbore. Radially severing a tubular member often requires lowering a downhole cutting tool, such as a tubing cutter, into the well bore for cutting the tubular member.
Various methods have been used to radially sever a tubular member. These methods include rotating cutting heads, electric arcs, cutting torches, and abrasive water jet cutting. In abrasive water jet cutting, a high velocity water jet is discharged through a jet nozzle. The velocity of the water may vary depending on need, but often ranges between 350 and 400 meters/second. The jet typically contains abrasive particles, which together with the high velocity water, cut the tubular member by abrasive action.
It can be difficult to determine when the radial cut about the circumference of the tubular member is complete. This may result in an incomplete cut, possibly requiring additional time spent re-cutting the tubular member. It may also result in an attempt to continue to cut even after the tubular member has been severed. One method used to address this problem has been to include a microphone near the cutting device. An operator may monitor the microphone and listen for a change in sound that may occur when the tubular member has been severed. This method has a number of drawbacks, including the difficulty in distinguishing the completion of the cut from the background noise, particularly in the noisy downhole environment, and variability in operator skill.